U.S. patent number 5,176,448 [Application Number 07/869,626] was granted by the patent office on 1993-01-05 for special injection and distribution device.
Invention is credited to Leonard T. King, Leo Nelmida.
United States Patent |
5,176,448 |
King , et al. |
January 5, 1993 |
Special injection and distribution device
Abstract
A stationary material mixing apparatus for mixing various
components in a fluid stream. The mixing apparatus is a biscuit
placed within a conduit along the longitudinal axis of the conduit.
The biscuit contains a plurality of openings therethrough where
within openings are located mixing elements which induce a
rotational angular velocity to the fluid stream. The material
mixing apparatus is particularly effective in mixing a low
viscosity component into a high viscosity fluid stream.
Inventors: |
King; Leonard T. (Long Beach,
CA), Nelmida; Leo (Lake Forest, CA) |
Family
ID: |
25353949 |
Appl.
No.: |
07/869,626 |
Filed: |
April 16, 1992 |
Current U.S.
Class: |
366/174.1;
366/339 |
Current CPC
Class: |
B01F
5/045 (20130101); B01F 2005/0034 (20130101) |
Current International
Class: |
B01F
5/04 (20060101); B01F 5/00 (20060101); B01F
015/02 (); B01F 005/06 () |
Field of
Search: |
;366/336,337,338,339,150,154,167,173,178 ;138/38,42 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Jenkins; Robert W.
Attorney, Agent or Firm: Wittenberg; Malcolm B.
Claims
I claim:
1. A stationary material mixing apparatus located within a
cylindrically-shaped conduit, said conduit having a longitudinal
axis and circular cross-section of a first diameter, said material
mixing apparatus provided for mixing a fluid stream with the
conduit and comprising a biscuit which is aligned along said
longitudinal axis, said biscuit possessing an upstream face and
downstream face, second diameter, and a plurality of openings where
within said openings are located mixing elements which induce a
rotational angular velocity to the fluid stream passing
therethrough, said apparatus being further characterized such that
substantially all of said mixing elements induce the same
rotational sign to said fluid, said biscuit supporting a frustum of
a cone emanating from the upstream face thereof and aligned along
said longitudinal axis, a feed leg radially emanating from the side
wall of said conduit downstream of said biscuit is provided which
is in fluid communication with a bore located within said biscuit
along said longitudinal axis thereof for discharge of a fluid from
an opening located at the apex of said frustum, said material
mixing apparatus being further characterized wherein said first
diameter of said conduit is greater than the second diameter of
said biscuit such that an annular gap is established substantially
uniformly between said biscuit and conduit.
2. The apparatus of claim 1 wherein said substantially uniform
annual gap is maintained by providing two or more protrusions
emanating from said biscuit.
3. The apparatus of claim 2 wherein said two or more protrusions
are of a substantially uniform height emanating from said
biscuit.
4. The apparatus of claim 3 wherein said protrusions are located in
at least two sets of three or more protrusions, each set being in
radial planes spaced substantially uniformly from said biscuit.
5. The apparatus of claim 1 wherein a first fluid is contained by
said conduit and a second fluid is introduced at the apex of said
frustum for mixing with said first fluid.
6. The apparatus of claim 5 wherein the specific gravity of said
first fluid is approximately at least 10% greater than the specific
gravity of said second fluid.
7. The apparatus of claim 6 wherein a portion of the first fluid is
caused to pass through said annular gap thus substantially
preventing said second fluid from contacting the side wall of said
conduit.
8. A method of mixing a second fluid of relatively low viscosity
into a first fluid of relatively high viscosity, said first fluid
passing within the interior bore of a cylindrically shaped conduit,
said conduit having a longitudinal axis and circular cross-section
of a first diameter, providing a material mixing apparatus within
the conduit comprising a biscuit aligned along said longitudinal
axis, said biscuit possessing an upstream face and downstream face,
second diameter sized smaller than said first diameter to provide a
substantially uniform annular gap between said biscuit and conduit,
and also possessing a plurality of openings wherein within said
openings are located mixing elements which induce a rotational
angular velocity to the fluid stream passing therethrough and same
rotational sign, said biscuit supporting a frustum of a cone
emanating from the upstream face thereof and aligned along said
longitudinal axis, a feed leg radially emanating from the side wall
of said conduit downstream and said biscuit and which is in fluid
communication with a bore located within said biscuit along said
longitudinal axis, passing said second fluid through said feed leg
and bore and discharging said fluid from said frustum so that
substantially all of said first and second fluids pass through said
plurality of openings and a portion of only said first fluid passes
through said annular gap.
Description
TECHNICAL FIELD OF THE INVENTION
The present invention deals with a material mixing apparatus which
contains various elements traditionally known as static mixers for
mixing components of a fluid stream. The mixer of the present
invention is uniquely designed to enhance the mixing of a low
viscosity component such as a colorant or dye into a high viscosity
fluid stream such as a polymer melt.
BACKGROUND OF THE INVENTION
It has long been realized that static mixers, if made to work
efficiently, provide certain economic advantages over dynamic
mixers for, as the name implies, static mixers employ no moving
parts. As such, static devices are generally less expensive to
configure and certainly much less expensive to maintain while
providing the user with an extended useful life for the mixer
product in service.
Prior art approaches to static mixers have generally involved
expensive machining, molding, casting or other fabrication of the
component mixer elements coupled with some type of permanent
attachment between elements and a conduit and/or between elements
within a conduit. The resulting cost and difficulty of
manufacturing results in a relatively expensive end product.
Moreover, many of the prior mixers provide less than complete
mixing, particularly with respect to material flowing along the
walls of the conduit. This so called "wall-smearing" is related to
the parabolic velocity profile of a fluid having laminar flow in a
pipe where the fluid velocity is small or zero along the wall
surfaces.
A marked improvement in static mixer technology was represented by
the teachings of Applicant's prior U.S. Pat. No. No. 3,923,288. The
invention embodied in the cited patent was taught to be a
stationary material mixing apparatus comprised of a plurality of
self-nesting, abutting and axially overlapping elements which are
fit into a conduit. Each region of axial overlap between elements
provides a mixing matrix introducing complex velocity vectors into
the materials.
In the case of a single input stream into an assembly of "n" mixing
elements such as those disclosed in U.S. Pat. No. 3,923,288, one
obtains 2.sup.n divisions of the stream. This is so because each
mixing element involves a 2.times.2 division of the flow
stream.
A device capable of increasing the mixing efficiency of mixing
elements such as those disclosed in the cited prior art to
something greater than 2.sup.n divisions was disclosed in
Applicant's U.S. Pat. No. 4,614,440. In its broadest terms,
Applicant's prior patent taught a stationary material mixing
apparatus for mixing a fluid stream which is in the shape of a
conduit comprising individual biscuit sections. The sections were
aligned along a common longitudinal axis, while each biscuit
section comprised a plurality of openings therethrough, where
within said openings are located mixing elements which induce a
rotational angular velocity to the fluid stream. Substantially all
of the mixing elements were taught to induce the same rotational
sign to the fluid whereby it was taught that openings in adjacent
biscuit sections were purposely misaligned to enhance the mixing
operation.
FIG. 1 represents a typical biscuit section as taught in
Applicant's prior U.S. Pat. No. 4,614,440. Biscuit element 10,
shown in plan view, is provided with a central opening 5 and
peripheral openings 6. A biscuit having a hexagonal hold
configuration with center hole 5 is typical of those biscuit
elements disclosed in Applicant's prior patent.
It was taught that virtually any mixing element could be placed
within openings 5, 6, etc., which in part induce a rotational
velocity to the fluid passing therethrough. Typical of such
elements are those disclosed in U.S. Pat. No. 3,923,288, the
disclosure of which is hereby incorporated by reference. Such
elements are depicted by numeral 13 of FIGS. 3 and 4, said elements
inducing or imparting the same rotational sign to the fluid passing
through the biscuit openings.
The sign of rotation of the mixed fluid is shown schematically by
elements 31 and 32 of FIG. 2. It was taught in Applicant's U.S.
Pat. No. 4,614,440 to provide a number of longitudinally aligned
biscuit elements, such as shown as elements 10, 11, etc., of FIG. 3
and to provide for openings in adjacent biscuit elements to be
misaligned. This misalignment is typified by the plan view of FIG.
2, whereby the geometric center of hole 6 coincides with the
periphery of hole 6a, the latter opening appearing in adjacent
biscuit element 11. This misalignment is the result of an
approximately 30.degree. shift between adjacent biscuits. It was
recognized that unless adjacent biscuit elements were misaligned, a
fluid injected into an upstream cell or opening, such as opening 6
of FIG. 1, would tend to channel its way through the various
downstream biscuit elements, and although the fluid stream would be
somewhat mixed, inter cell mixing would not occur. By misaligning
biscuit elements such as shown in FIG. 2, each cell of, for
example, biscuit 11 would accept or capture material from two cells
of biscuit 10, and as such, mixing would be enhanced. As all
helical mixing elements 13 are provided with the same sign, the net
result of misalignment is to divide and recombine the product many
times since each section having helical holes splits and recombines
the flow of fluid 12 times.
It was further recognized that as a means of enhancing the mixing
phenomenon, it was found preferable to block openings in various
biscuit sections. Ideally, the blocked openings were located in
alternative biscuits, that is, not in adjacent biscuits and, most
preferably, blocked openings would be located in the geometric
centers of the various biscuits. FIG. 4 is illustrative of this
embodiment wherein biscuits 10, 11 and 12 are shown in exploded
perspective view whereby fluid stream 17 is shown emanating from
center hole 5 of biscuit element 10. Without the blockage of center
hole 5a of biscuit 11, the fluid traveling along path 17 would tend
to burrow through all of the longitudinally aligned center openings
5, 5a and 5b without any adjacent hold mixing. By blocking center
hole 5a, fluid stream traveling through the center opening 5 was
caused to proceed through openings 6a and 7a of biscuit 11 and
assume path 17a, 17b, etc., prior to encountering biscuit 12. At
biscuit 12, fluid stream 17a and 17b was broken up even further for
now center hole 5b, being unplugged, would accept fluid as well as
adjacent mixing openings.
When one or more of the center openings in the system were blocked,
it was taught to be preferred to space biscuit elements from one
another to enable fluid downstream from a biscuit containing a
blocked opening to encounter an unblocked, centrally located
opening therein. FIG. 3 is referred to as being illustrative of the
invention disclosed in Applicant's U.S. Pat No. 4,464,440 whereby
biscuits 10, 11, etc., nested within conduit 20 are notched to
provide a nesting or interlocking relationship. Further, internal
spacing 40 was provided to enable proper fluid handling in and
around biscuits containing centrally blocked openings, which
further reduced the pressure drop along the overall conduit.
The stacked motionless mixing device comprising various biscuit
sections 10, 11, etc., provided a vastly superior mixing device
from that contemplated by the prior art. For example, in the case
of a single input stream into an assembly of "n" mixing elements,
such as those shown in U.S. Pat. No. 3,923,288, one would obtain
2.sup.n divisions of the input stream. However, in practicing the
invention shown in U.S. Pat. No. 4,614,440, a 2-inch mixer would
behave like a 2.sup.2n mixer. If one were to provide six peripheral
holes in an eight biscuit conduit, instead of having a
6.times.2.sup.n which equals 6.times.256, one would have
6.times.2.sup.16, which equals 6.times.65536. The improvement
factor thus achieved in practicing that invention would be
represented by the fraction 65536/256 or 256.
It was taught in Applicant's now abandoned application Ser. No.
184,453, filed on Apr. 18, 1988, that the stacked motionless mixer
described in Applicant's U.S. Pat. No. 4,614,440 could be
particularly advantageous in the introduction of very small
quantities of low viscosity liquids into very high viscosity
extrudate melt systems or other high viscosity fluid streams if
certain modifications were made which constitute the contribution
of the present invention. The introduction of a low viscosity
liquid such as a liquid colorant or lubricant to be added to a
polymer stream, is quite difficult, for with most static mixer
technology, small quantities of the low viscosity additive tend to
tunnel through the mixer without being properly mixed.
Attempts have been made to solve this problem by introducing the
low viscosity additions by multi-hold spargers or slotted sparger
pipes. This approach is simply inadequate for the higher viscosity
material governs the flow patterns and such devices will only
operate at one flow rate for uniform additive distribution from the
holes or slots. Asymmetrical plugging of the additive holes or
slots invariably occurs.
Applicant disclosed yet a further embellishment to the
above-described mixing device in its U.S. patent application Ser.
No. 313,443, filed on Feb. 22, 1989, now abandoned. That
application disclosed a mixing device which incorporated an
individual biscuit section which was aligned across the
longitudinal axis of the conduit. The biscuit possessed a plurality
of openings wherein within each opening was located mixing elements
which would induce a rotational angular velocity to the fluid
stream passing therethrough wherein all of the mixing elements
induced the same rotational sign to the fluid. This device is shown
in FIGS. 5 and 6 wherein element 33 is shown located within conduit
20 to confront main fluid stream traveling in the direction of
arrows 34. Also shown, for the first time, was the use of forward
and rear faces 51 and 52 of biscuit element 33 which are sloped to
prevent "dead spots" on the face of the biscuit element from acting
as fluid shelves, trapping fluid components which otherwise were
intended to pass through the biscuit element to become part of the
mixture.
FIG. 5 shows fluid entry port 29 fed to the apex of
conically-shaped plug 21 which was aligned along the longitudinal
axis of biscuit 33 and cylindrical conduit 20. As such, the apex of
conically-shaped plug provided the first point of contact of fluid
emanating from fluid entry port 29.
In the embodiment of FIG. 5, fluid entry port 29 was fed via feed
leg 27 which passed through conically-shaped conduit 20 and
extended radially within the conduit. In the embodiment of FIG. 5,
second leg 28 was deployed substantially along the longitudinal
axis of conduit 20 which oriented the fluid emanating from fluid
entry port 29 in the direction of main flow 34.
As shown in FIG. 6, yet another embodiment of the invention was
disclosed whereby fluid entry port 37 was shown as being an
integral part of conically-shaped plug 21a. In this embodiment,
fluid emanating from entry port 37 was fed from a first leg 35
which passed through conically-shaped conduit 20 and which extended
radially within biscuit 33 and through a second feed leg 36 which
extended from first feed leg 35 along the longitudinal axis of the
biscuit for the discharge of fluid substantially at the apex of the
conically-shaped plug 21a. It was the intent of Applicant in
providing the embodiment of FIG. 6 to provide a feed point 37
enabling fluid to spill over conically-shaped plug 21a uniformly
about the surface of this conically-shaped member providing a
waterfall effect for feeding each of orifices 6, etc., with
substantially equal amounts of this fluid.
Although the various embodiments disclosed above provided a vast
improvement over preexisting mixing devices particularly when
dealing with the introduction of very small quantities of low
viscosity liquids into very high viscosity extrudate melt systems
or other high viscosity fluid strains, certain deficiencies
remained which require rectification. For example, when the device
shown in FIG. 5 was employed, great care had to be exercised to get
the injection point exactly aligned with the center of the biscuit.
This was found to be particularly critical at very low flow rates
of additive. Any misalignment would result in the additive
tunnelling down one side of the biscuit rendering the device
ineffective.
In addition, it was found that when the specific gravity of the
additive was very different from that of the main flow, for
example, when a difference of 10 percent or more existed and when
the viscosity of the additive was very low, surface tension became
an important factor. Additive which touched the side walls of the
conduit was moved by capillary attraction, either up or down the
conduit walls to accumulate along the upper or lower region of the
conduit, depending upon its specific gravity relative to the main
flow. This phenomenon was obviously detrimental to the effective
mixing of the various components
It is thus an object of the present invention to provide a device
which overcomes and substantially rectifies the problems recited
above.
This and further objects will be more readily appreciated when
considering the following disclosure and amended claims
wherein:
FIGS. 1 through 6 represent prior art devices discussed above.
FIG. 7 depicts, in cross-section, the mixer apparatus of the
present invention.
FIG. 8 is an illustration of the output pattern of additive
emanating from the mixing device of the present invention.
SUMMARY OF THE INVENTION
The present invention deals with a stationary material mixing
apparatus as well as for a method of using this apparatus for
mixing two or more fluids. The stationary material mixing apparatus
is located within a cylindrically-shaped conduit, the conduit
having a longitudinal axis and circular cross-section of a first
diameter.
The material mixing apparatus comprises a biscuit which is aligned
along the longitudinal axis of the conduit. The biscuit possesses
an upstream face and downstream face, a second diameter, and a
plurality of openings where within each opening is located mixing
elements which induce a rotational angular velocity to the fluid
stream passing therethrough. The apparatus is further characterized
such that substantially all of the mixing elements induce the same
rotational sign to the fluid.
The biscuit supports a frustum of a cone emanating from its
upstream face. The frustum is aligned along the longitudinal axis
of the conduit.
A feed leg is provided extending radially from the side wall of the
conduit downstream of the biscuit. The feed leg is in fluid
communication with a bore located within the biscuit along the
longitudinal axis thereof for the discharge of fluid from an
opening located at the apex of the frustum.
The present material mixing apparatus is characterized such that
the first diameter of the conduit is greater than the second
diameter of the biscuit. As such, a substantially uniform annular
gap is established between the biscuit and conduit.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 7, a stationary material mixing apparatus 72 is
shown located within cylindrically-shaped conduit 71 having a
longitudinal axis 90 and a circular cross-section best seen by
referring to FIG. 8. The biscuit or material mixing apparatus 72 is
aligned along longitudinal axis 90 while possessing upstream face
91 and downstream face 92 and a second diameter. A plurality of
openings (not shown) are established within the biscuit in a manner
depicted by the individual biscuit elements 10, 11 and 12 of FIG. 4
which contain mixing elements which induce a rotational angular
velocity to the fluid stream passing therethrough. As noted
previously, the apparatus is characterized such that substantially
all of the mixing elements induce the same rotational sign to the
fluid.
Biscuit 72 supports a frustum of a cone 77 emanating from upstream
face 91. The frustum is aligned along longitudinal axis 90 as shown
in FIG. 7.
Feed leg 73 is shown emanating from side wall of conduit 71
downstream of biscuit element 72. Feed leg 73 is in fluid
communication with bore 74 located within biscuit 72 along
longitudinal axis 90. As such, a low viscosity additive can be
introduced to the main flow within conduit 71 through feed leg 73,
bore 74 and an opening located at the center of frustum 77 as shown
by virtue of arrow 75.
Conduit 71, as noted previously, is characterized as having a
circular cross-section of a first diameter as shown in FIG. 8.
Material mixing apparatus or biscuit 72 also has a circular
cross-section of a second diameter, smaller than the conduit's
first diameter. As such, an annular gap is established
substantially uniformly between the biscuit and conduit. As a
preferred expedient, to maintain that gap, protrusions 79 and 80
are provided. These can be established conveniently by welding sets
of buttons on the outside of biscuit 72 followed by machining the
buttons to get all of them to the same height. Ideally, an annular
gap of approximately two percent of the conduit's inside diameter
has been found to work well in the practice of the present
invention.
It has been found that the device of the present invention causes
the additive emanating from frustum 77 to be distributed as thin
radial sheets 78 (FIG. 8). This produces a larger interfacial
surface area between the additive and the main component flow
within the conduct.
It was found that when a device such as shown in FIG. 5 was
employed, great care had to be exercised to be sure that the
injection point of the additive was exactly aligned with the center
of the biscuit module. This was found to be particularly critical
at very low flow rates of additive, on the order of less than one
percent. If this was not done, the additive tended to tunnel down
one side of the biscuit rendering the mixing apparatus
ineffective.
It was also found that when the specific gravity of the additive
was very different from that of the main flow, for example, 10
percent or more, and when the additive exhibited a very low
viscosity, surface tension came into play. Additive which touched
the walls of conduit 71 moved by capillary attraction, either up or
down on the conduit walls, to accumulate along the upper or lower
regions of the conduit, depending upon its specific gravity
relative to the main flow.
The present invention eliminates the difficulties recited above by
introducing the additive downstream of biscuit 72 and by providing
the above-recited substantially uniform annular gap. The latter
expedient enables a portion of the main flow to travel through the
annular gap outside and around biscuit 72 which prevents the
downstream or output additive sheets 78 from contacting conduit 71
sidewalls.
Furthermore, by injecting additive through the centrally located
opening of frustum 77, alignment problems such as those experienced
in practicing the invention shown in FIG. 5 are eliminated. By
employing the mixing apparatus of FIG. 7, one is ensured of always
having uniform distribution of additive throughout biscuit 72.
* * * * *